1. Technical Field
The present invention relates generally to addressable, reusable, twisting ball displays.
2. Description of the Related Art
A twisting-ball display, also known as a xe2x80x9cgyricon,xe2x80x9d is an addressable display made up of a multiplicity of optically anisotropic balls, each of which can be selectively rotated to present a desired face to an observer. For example, one such display comprises balls each having two distinct hemispheres, one black and the other white, with each hemisphere having a distinct electrical characteristic (e.g., zeta potential with respect to a dielectric fluid) so that the balls are electrically and optically anisotropic. The balls are embedded in a sheet of optically transparent material, such as an elastomer layer, that contains a multiplicity of spheroidal cavities and is permeated by a transparent dielectric fluid, such as a plasticizer. The fluid-filled cavities accommodate the balls, one ball per cavity, to prevent the balls from migrating within the sheet. A ball can be selectively rotated within its respective fluid-filled cavity, for example by application of an electric field, so as to present either the black or the white hemisphere to an observer viewing the surface of the sheet. Thus, by application of an electric field addressable in two dimensions (as by a matrix addressing scheme), the black and white sides of the balls can be caused to appear as the image elements (e.g., pixels or subpixels) of a displayed image.
The above-described twisting ball panel display was first described in U.S. Pat. No. 4,126,854 to Sheridon. The original technology, which was constructed of black-and-white balls, could not provide a multicolor image. As a reult, over the last several decades, there have been several improvements to the original design. Thus, for example, U.S. Pat. Nos. 5,344,594 and 5,708,525 describe a multisegmented ball useful fox producing a colored display. In these patents, a representative gyricon ball has up to 2N segments n arbitrary color combinations. Black, white, or other color pigments or dyes can be used, alone or in combination, so that segments can be made in different colors or shades. The patent also teaches that segments can be made clear by using unpigmented, undyed plastic liquid, and that different segments can be made to have different widths.
In the prior art, as illustrated in FIGS. 3C-3D of U.S. Pat. No. 5,708,525, the colored segments of a multichromal ball are symmetric around the ball""s vertical axis. This symmetry is required because the electric field addressing schemes do not have the capability of positioning the ball longitudinally. As a consequence, any given ball may only include a relatively small number of colors. This significantly limits the flexibility of the overall display. An alternate approach to producing a colored display is to use several balls per pixel to form a given color, such as illustrated in U.S. Pat. No. 5,767,826. The latter approach, however, reduces resolution and complicates manufacturing because the balls must be individually placed.
There remains a need in the art to advance the twisting ball display art to provide a more full range of colored displays and, more particularly, to enhance the control over individual ball elements.
It is an object of the present invention to provide an electrical and magnetic. twisting ball display device made up of spheroidal, multichromal balls.
It is another more particular object to use an field and a magnetic field to control the individual position of a given ball in a twisting ball display. The ball has both an electric dipole and a magnetic dipole.
It is yet another object of this invention to provide a mechanism for selectively positioning a spheroidal ball of a twisting ball display both latitudinally and longitudinally.
Still another object of the present invention is to construct a colored ball display sheet wherein each ball is both an electret and magnet. This permits the application of a combination of electric and magnetic fields to orient a given surface of the ball to a desired position.
A more general object is to provide twisting colored ball displays with higher resolution.
Another object of the present invention is to provide electric paper with individually addressable electret and magnetic balls.
Yet another object of this invention is to provide paper-like digitally addressed media that has various applications including, without limitation, a colored display, a sheet of electric paper, an overlay transparency, or an architectural screen.
It is another object of this invention to a paper-like digitally addressable sheet material that retains a displayed image in the absence of power.
These and other objects are provided in an addressable display device comprising a light transparent body having a plurality of spheroidal balls supported therein, and addressing means for selectively applying an electric field and/or a magnetic field across a selected portion of the body to position a given ball relative to a viewing direction. Preferably, a given ball is multichromal and, in one embodiment, includes at least a first color within a first longitudinal range, and a second color within a second longitudinal range. The color located within a given longitudinal range may have different saturation throughout the range. Thus, for example, the first longitudinal range includes red within a first latitude range thereof and pink within a second latitude range.
A given spheroidal ball has an anisotropy for providing an electrical dipole moment, and an anisotropy for providing a separate magnetic dipole moment. The electrical dipole moment renders the ball electrically responsive such that, when the ball is subjected to an electric field, the ball rotates toward an orientation in which the electric dipole moment aligns with the electric field. Likewise, the magnetic dipole moment renders the ball""s magnetic response such that, when the ball is subjected to a magnetic field, the ball rotates to an orientation in which the magnetic dipole moment aligns with the magnetic field. Selective and/or sequential application of the electric field and/or the magnetic field thus serves to position a given region of the ball a particular orientation. The given region typically includes a color. In operation, the ball is selectively rotatable within a transparent body to position a given color with respect to a viewer or light modulating source.
In a preferred embodiment, the addressing means comprises an array of electrical conductors, with each position in the array being associated with a spheroidal ball. The electrical conductors, for example, comprise a set of first, second and third conductors. In one embodiment, the first conductor is positioned on a first surface of the light transparent body along a first direction and includes a coil portion extending therefrom for generating the magnetic field. The second and third conductors are positioned on a second surface of the light transparent body (opposite the first surface) along a second direction transverse to the first direction. These conductors generate the electric field. A pair of diodes connect the coil to the second and third conductors, and the spheroidal ball is preferably located within the confines of the coil. The particular orientation of the ball, both laterally and longitudinally, is determined by given signals applied to the first, second and third electrical conductors.
The foregoing has outlined some of the more pertinent objects and features of the, present invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention as will be described. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the following Detailed Description of the Preferred Embodiment.